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NCL (NCAR Command Language)

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NCL (NCAR Command Language)
NameNCL
DeveloperNational Center for Atmospheric Research, University Corporation for Atmospheric Research
Released1990s
Programming languageC (programming language), Fortran
Operating systemUnix, Linux, macOS, Microsoft Windows
LicenseBSD licenses

NCL (NCAR Command Language) is a domain-specific scripting language designed for the analysis and visualization of geoscientific data, developed primarily by the National Center for Atmospheric Research and distributed via the University Corporation for Atmospheric Research. It integrates numerical computation, file I/O, and graphics into a cohesive environment used across research institutions such as the National Oceanic and Atmospheric Administration, NASA, and numerous universities including University of California, Berkeley, Princeton University, and Massachusetts Institute of Technology.

Overview

NCL provides a specialized toolset for handling multidimensional arrays, time series, and grid-based data common to projects at NOAA, NASA Goddard Space Flight Center, European Centre for Medium-Range Weather Forecasts, Los Alamos National Laboratory, and Jet Propulsion Laboratory, enabling scientists from Columbia University, University of Washington, University of Colorado Boulder, Scripps Institution of Oceanography, and Imperial College London to produce publication-quality graphics and diagnostics. The software suite interoperates with formats and systems such as NetCDF, HDF5, GRIB, OpenDAP, MPI, and tools developed at institutions like Lawrence Berkeley National Laboratory and Argonne National Laboratory.

History and Development

Development began in the 1990s at the National Center for Atmospheric Research with contributions from staff affiliated with University Corporation for Atmospheric Research and collaborators at NOAA and NASA. Over time, contributions and user needs from research groups at CERN, NCAR, NIST, NOAA Geophysical Fluid Dynamics Laboratory, and academic laboratories including Caltech and Yale University shaped the language, integrating advances from Fortran libraries, C (programming language) backends, and I/O standards like CF (climate and forecast) metadata convention and OGC. Governance and distribution were influenced by open-source practices at organizations such as Free Software Foundation and licensing paradigms used by BSD-licensed projects at Berkeley Software Distribution.

Features and Capabilities

NCL offers built-in support for array-oriented operations, statistical analysis, regridding, and interpolation routines used by teams at ECMWF, NOAA NCEI, NASA Goddard, Rutgers University, Purdue University, and University of Texas at Austin. It includes graphics primitives, map projections, contouring, and vector plotting comparable to libraries developed at NCAR Research Applications Laboratory and tools used in projects at Princeton Plasma Physics Laboratory and Oak Ridge National Laboratory. The environment integrates metadata handling compliant with conventions maintained by World Meteorological Organization and data stewardship practices at USGS and NSF-funded centers.

Syntax and Programming Model

The language uses an imperative scripting model with data structures and control flow familiar to users from Fortran and array languages used in research groups at MIT Lincoln Laboratory and Lawrence Livermore National Laboratory. It supports user-defined functions, modular workflows, and batch processing patterns adopted by labs such as NOAA ESRL and university research clusters at University of Michigan and Cornell University. Interoperation with external libraries is achieved through interfaces similar to those used by projects at Argonne National Laboratory and Sandia National Laboratories.

Graphics and Visualization

NCL's graphics system produces contour plots, filled contour maps, vector fields, and composite figures used in publications by researchers at Nature (journal), Science (journal), Proceedings of the National Academy of Sciences, and conference presentations at American Geophysical Union and American Meteorological Society. It supports map projections and coastlines maintained by cartographic projects at NOAA and Natural Earth, and generates output in formats compatible with workflows at IEEE and editorial pipelines at Wiley. Visualization capabilities parallel those in software from ESRI, Matplotlib, GMT (Generic Mapping Tools), and tools employed at NCAR visualization groups.

Data Formats and I/O

NCL reads and writes scientific data formats such as NetCDF, HDF5, and GRIB used by operational centers including ECMWF, NOAA NCEP, Met Office, and satellite data archives at NASA EOSDIS. It supports remote access protocols like OPeNDAP and integrates with cataloging systems associated with ESGF and archives at NOAA NCEI and PANGAEA. Metadata handling aligns with standards promulgated by GCMD and community practices at World Data System.

Performance and Extensibility

Performance-sensitive routines are implemented in compiled languages with designs influenced by high-performance computing centers such as Argonne National Laboratory and Oak Ridge National Laboratory, and parallelization strategies align with MPI and cluster use at XSEDE and national supercomputing facilities like NERSC. Extensibility is supported via linking to external libraries, plugin mechanisms used at Unidata, and interoperability with scientific stacks maintained by communities around SciPy, NumPy, and software repositories at GitHub.

Use Cases and Community Adoption

NCL is used in climate diagnostics, model intercomparison projects coordinated by CMIP, seasonal forecasting efforts at NOAA Climate Prediction Center, and observational analyses by groups at NASA, JPL, Scripps Institution of Oceanography, Lamont–Doherty Earth Observatory, Potsdam Institute for Climate Impact Research, and many university research teams. Training and documentation have been disseminated at workshops hosted by AGU, AMS, UCAR, and through community forums connected to ESIP and educational programs at institutions like Columbia University and University of Oxford.

Category:Scientific software